In the related art, Japanese Unexamined Patent Publication No. 2016-15137 is known as a technical literature relating to a system considering a state of a driver. In the literature, an autonomous travelling system for a vehicle is disclosed, which calculates a lead time that is a remaining time for an autonomous travelling to be surely continued and a reaction time for the driver to intervene in the autonomous driving (a countermeasure for a manual driving). In this system, when a comfort time which is a difference between the lead time and the reaction time becomes zero, a countermeasure to the driver such as a warning is performed.